Postfix MTA
From MyWiki
Inspecting the mail queue. http://www.tech-g.com/2012/07/15/inspecting-postfixs-email-queue/
http://divideoverflow.com/2015/10/Making-SSMTP-authenticate-with-certificate-to-postfix/ ( cidr format and sasl )
https://wiki.centos.org/HowTos/postfix_restrictions
